Magnesium base alloy



Patented Mar. 4, 1941 MAGNESIUM BASE ALLOY John C. McDonald, Midland, lllich, assignor to The Dow Chemical Company, Midland, Mich.,

. a corporation of Michigan No Drawing.

strengths.

Magnesium alloys are being widely used in various structural and mechanical arts where a light weight metal is highly desirable, such as for use in making castings, forgings, and the However, the use of these alloys in the rolled form to make sheet metal articles requiring forming operations, such as bending, drawing, and the like, has not progressed as rapidly due to the fact that in general alloys of good formability, permitting relatively sharp bends to be made without the article developing external cracks, usually have inferior strength charlike.

acteristics.

strengths.

Other objects and advantages will be apparent as the description of the invention proceeds.

My invention resides in the discovery that a Application March 30, 1940,

Serial No. 327,033

3 Claims. (0 75-168) composition indicated, I have found that in general the preferred combination of properties is obtained when the alloy contains from about 2 to '7 per cent of aluminum, from about 0.05 to 0.4 per cent of calcium, and from about 3 to 10 per cent of thallium.

The specific proportion of each alloying metal and the total amount to be added to the new alloy depends upon the use for which the alloy is intended. For example, where exceptionally high ductility or formability associated with good yield and tensile strengths is highly desirable, the alloy should preferably contain from about 1 to 3 per cent of aluminum, from 0.1 to 0.2 per cent of calcium, and from 3 to 7 per cent of thallium. In those instances where higher yield and tensile strengths are more important, the alloy should contain proportionately larger amounts of aluminum and thallium.

The following table lists some of the properties of rolled sheet metal made from my new quaternary alloy and compares these properties with those of rolled sheet made from closely related ternary alloys. A comparison of the properties illustrates the improvement in the strength characteristics of the new alloy over that of the closely related ternary alloys. In the table, the per cent elongation is to be regarded as a measure of the ductility or formability of magnesium base alloy composed of from 0.3 to the article. 12 per cent of aluminum, from 0.01 to 1 per cent Table Nominal composition in percent (magnesium=remainder) Annealed Cold rolled Yield Tensile Percent Yield Tensile A1 Ca Tl strength in strength in elongation strength in strength in lbs./sq. in lbsJsq. in. in 2 inches lbs./sq. in lbs./sq. in.

..... 0. 20 5. 0 21, 000 35, 000 15 34, 000 37, 000 1. 1 5. 0 1 000 32, 000 16 32, 000 39,000 1. 1 0. 20 20, 000 33, 000 16 31, 000 38, 000 1. l 0. 26 5. 0 21, 000 35, 000 20 34, 000 42, 000 0. 20 10. 0 19, 000 34, 000 16 30, 000 000 1. 2 10. 0 19, 000 33, 000 20 32, 000 39, 000 l. 2 0.20 20, 000 33, 000 16 31, 000 38, 000 l. 2 0. 34 10.0 21, 000 35, 000 20 35, 000 42, 000 0. 20 5.0 21, 000 35, 000 15 31,000 37, 000 2. 5 0. 20 24,000 35, 000 17 35, 000 41, 000 2. 5 0. 28 5. 0 21,000 36, 000 20 40, 000 47, 000 0. 20 10. 0 19, 000 34, 000 16 30, 000 36, 000 4. 8 0. 20 25, 000 39, 000 15 39, 000 45, 000 4. 8 0. 28 10. 0 27, 000 43, 000 18 42, 000 000 of calcium, from 1 to 20 per cent of thallium, the balance being substantially all magnesium, is endowed with the aforementioned properties. While the properties of good formability or ductility associated with excellent tensile and yield strengths are manifest over the entire range of The properties listed in the above table under the section headed by the term Annealed were obtained by first rolling the alloys at a temperature of 450-650 F. and thereafter annealing them at various temperatures in a temperature range or 400M300 F. The properties selected .high. Similar improvement will for the table were those 01' the annealed specimens which exhibited the maximum elongation. The properties listed in the above table under the section headed by the term "Cold Rolled were obtained by subjecting specimens of the alloy which had been hot rolled at a temperature of from 450 to 650 F. to additional rolling in the cold state in order to improve their strength characteristics. The properties selected for the table were those of the cold rolled specimens which showed the greatest tensile and yield strengths while having at least a 1 per cent elongation in 2 inches.

By a comparison of the properties listed in the above table, it will be observed that the combined properties of my new quaternary alloy are superior to those of the ternary alloys having similar percentages of alloying ingredients, For example, it will be noted that when the alloy contains the lower percentages of alloying metals it has a very high elongation value coupled with markedly superior strength properties in both the cold rolled and the annealed state. As higher percentages of alloying metals are included in the alloy, the strength characteristics show a. marked improvement while the formability stillremains be noted throughout the range of alloying ingredients indicated.

While the new alloy is most useful in the wrought form, such as sheets, due to its formability characteristics, it may also be-used in making castings, forgings, extruded forms, and the like. It is further pointed out that the new alloy is amenable to conventional solution and precipitation heat treatments, which, accordingly, modify its properties.

The new alloy may be compounded in any of the ways known in the art, such as by adding the alloying ingredients to molten magnesium maintained under a suitable flux. The flux should be substantially free from magnesium chloride if the calcium content is to be above 0.3 per cent. In those instances where the calcium content is to be less than 0.3 per cent, magnesium chloride may be present in the flux without exerting any harmful effects, but in this case it is preferable to add the calcium last and without too much stirring or agitation in order to prevent loss of some of the calcium into the flux.

I claim:

1. A magnesium base alloy containing from 0.3 to 12 per cent of aluminum, from, 0.01 to 1.0 per cent of calcium, and from 1 to 20 per cent of thallium, the balance being magnesium.

2. A magnesium base alloy containing from 1 to 3 per cent of aluminum, from 0.05 to 0.4 per cent of calcium, and from 3 to 7 per cent of thallium, the balance being magnesium.

3. A magnesium base alloy containing from 8 to 10 per cent of aluminum, from 0.05 to 0.4 per cent of calcium, and from 3 to 7 per cent thallium, the balance being magnesium.

JOHN C. McDONALD. 

